Documentation: ABI: testing: ad485x: add ABI docs

Add documentation for the packet size.

Signed-off-by: Antoniu Miclaus <[email protected]>

Author: amiclaus

Documentation/ABI/testing/sysfs-bus-iio-adc-ad485x

@@ -0,0 +1,14 @@
+What:		/sys/bus/iio/devices/iio:deviceX/packet_format_available
+KernelVersion:
+Contact:	[email protected]
+Description:
+		Packet sizes on the CMOS or LVDS conversion data output bus.
+		Reading this returns the valid values that can be written to the
+		packet_format.
+
+What:		/sys/bus/iio/devices/iio:deviceX/packet_format
+KernelVersion:
+Contact:	[email protected]
+Description:
+		This attribute configures the packet size.
+		Reading returns the actual size used.